1. Field of the Invention
The present invention relates to a light emitting element driving device arranged to drive a light emitting element, and a light emitting device and a vehicle using the light emitting element driving device.
2. Description of Related Art
A light emitting device including a series connected body constituted of a plurality of light emitting diodes is used for a headlight of a vehicle, for example. In order to realize an adaptive front-lighting system (AFS) or an adaptive driving beam (ADB) when the light emitting device is used for a headlight of a vehicle, it is preferred to dispose short-circuiting switches respectively in parallel with the light emitting elements of the series connected body and to turn on and off the short-circuiting switches so that the number of turned-on light emitting diodes can be controlled.
The light emitting device including the series connected body constituted of a plurality of light emitting diodes, in which the number of turned-on light emitting diodes can be controlled by turning on and off the short-circuiting switches, usually includes separately a substrate on which a light emitting element driver IC is mounted and a substrate on which the series connected body constituted of a plurality of light emitting diodes, the short-circuiting switches, and a switch controller arranged to control the short-circuiting switches are mounted, and hence the light emitting element driver IC and the switch controller cannot be synchronized with each other in general. For this reason, in order to set the number of turned-on light emitting diodes to zero, it is common that the switch controller turns on all the short-circuiting switches.
A light emitting device usually has a ground fault protection function (see, for example, JP-A-2012-71712), and an output of the light emitting element driver IC is stopped when a ground fault is detected.
However, in the light emitting device including the series connected body constituted of a plurality of light emitting diodes, in which the number of turned-on light emitting diodes can be controlled by turning on and offthe short-circuiting switches, when the number of turned-on light emitting diodes is set to zero, a short circuit similar to a ground fault due to abnormality is formed by the short-circuiting switches. For this reason, when the ground fault protection function is mounted in the light emitting device including the series connected body constituted of a plurality of light emitting diodes, in which the number of turned-on light emitting diodes can be controlled by turning on and off the short-circuiting switches, unless the light emitting element driver IC recognizes the control content of the switch controller, the case of setting the number of turned-on light emitting diodes to zero may be misdetected as a ground fault due to abnormality so that the protection may be performed.